Blew out 2nd oil filter

[dsfnctn]

I am helping with a 2.8 motor that the oil filter blew out. We cleaned up the engine and replaced the filter and it ran fine. started it up and the pressure seemed ok on the gauge and then ran up between 3-4 k and the filter blew again. The engine has about 8k on it since rebuild. After removing the engine and cleaning I am ready to check the by pass valves. Has anyone had such a problem?

[patkeefe]

Filter is on the scavenge side of the pump, which doesn't make that much pressure. Do you have a restriction between the tank and the pickup tube in the sump, perhaps?

[Steve@Rennsport]

Using Mahle oil filters?

How much pressure did you see on the gauge, both cold & hot??

Oil viscosity?

Does this engine case have the correct bypass & relief pistons, springs & shims?

[neilca]

Filters on the scavange side will blow up because the initial surge of oil is like a brick wall hitting the filter. It is true that the scavange side is low pressure in a steady state condition. I plumbed in an external high pressure relief valve that bypassed the filter until the pressure dropped. If you study the stock system you will find a high pressure bypass built into the stock oil filter console that dumps the high pressure oil straight into the tank.

[Walt Fricke]

Someone once told me he plumbed an oil pressure gauge into his scavange pump line, and was astounded at how much pressure it recorded. I don't think it can properly be called low pressure. Lower, but not low. The cold oil effect would only increase this.

Were these stock oil coolers? I've had some crushing on my Canton Mecca filter inserts despite trying to get some temperature into the oil before going to WOT. But the Station 1 filters (pleated stainless mesh) which I use on both sides of the pump have never shown anything like this. But that may be because they, like the stock Mahle, have an overpressure relief feature built in.

[patkeefe]

I have my engine on my test stand at the moment. I have gauges on the scavenge line at the filter, the pressure side and the turbo feed line. They are hard to see in this photo, but when I run it again, I will note the pressures. I have a manual bypass piped on this stand; the AN-16 line from the scavenge pump tees into two AN-12. I think the scavenge gauge reads pressure leaving the filter...I forgot, so I'll have to check it.

[dsfnctn]

Thanks all of you for your years of knowledge and wisdom. It means a lot to me.
We have the engine all cleaned up and appreciate the help. The car is sort of custom and it is built on 72 car. The thermostat is in the nose of the car and i wondering if this freight train affect might hav been part of the problem since after start i had the car idling to sort out the slide valves and then when i ran to 3k the oil came in like a broken dam into the filter.

[Daves911L]

Interesting problem. I would imagine the scavenge pump is capable of producing exactly the same pressure as the pressure pump. They are after all precisely the same design. The different sizes would result in different volumes pumped at a given rpm/pressure, but wouldn't change the maximum pressure the pump is capable of generating. The scavenge circuit generally is at lower pressure because that pump is moving its volume into large passageways (about 20 mm if I recall correctly) which ultimately dump, via the filter, into the oil tank. With the exception of the filter, there isn't much to cause pressure to build in that circuit. The pressure pump on the other hand directs its flow through much smaller passages which terminate in planned "leaks", and pressure rises quickly to the limit of what can go through those leaks.

In your specific case the problem is likely to do with pressure relief at the oil filter console (not those in the engine case). The original oil filter console has a pressure relief valve built into it to prevent bursting the filter, which is quite likely when attempting to pass cold oil through the filter, and possibly even warm oil at higher rpm. You mention a custom design, so perhaps the filter console is not original and lacks a pressure relief valve? Or maybe the pressure relief valve is damaged or stuck.

[KTL]

Is the blown filter on the pressure side of the system, where the engine mounted oil cooler typically resides? If so, and you have removed the engine's internal t-stat, and the filter you are using doesn't have an effective bypass, then I can see how the filter can be compromised.

But a filter with internal bypass that is located on the tank shouldn't blow because it's overpressure dumps into the tank like Neil said. There's also a pressure relief valve in the oil filter console if you have the original '72 oil tank. There's also a pressure relief valve in the external t-stat, depending on which type you are using.

The typical Mahle filters used on the scavenge side has an internal bypass. The external t-stat also has a pressure relief valve built into it. The factory external t-stats (both the 74-89 version and the 89-94 964 version) are very good t-stats in my opinion because they have that pressure relief function in them to protect the cooler. I have always wondered how many people have problems with using the nice quality, more economical Mocal t-stats because they don't have a bypass function in them.

Also, I believe you want to locate your external t-stat as close to the engine as possible like Porsche did. The way the external t-stat works is the open/close function is on the return side of the t-stat. Meaning, the oil flows thru the t-stat & thru the cooler and is stopped on the return entry into the t-stat. So oil backs up in this oil path until the t-stat is warmed enough to turn off the short low temp circuit and activate the flow thru long circuit w/ the cooler.

I don't think the long path to the cooler is the problem (Porsche did it this way for a very long time so there must be a good reason to do it) since this oil is just sitting there in the lines getting slowly warmed by the hot oil pushing against it way back at the t-stat. Plus that partially warmed oil is being cooled by the front cooler a little bit. Not much, since the cooler is not passing any oil yet.

However, if you locate the t-stat quite far from the tank way up front at the front cooler? You have a much longer scavenge path leading to your tank and filter and this can be problematic when cold?

[Dan J]

Do you have an additional cooler? If so do you have a thermostat? If no you should add one
What oil were you using? What was the ambient temp? I have seen this happen on modified 72's with no thermostat and thick oil

[john walker's workshop]

i see a fram filter.....

[dsfnctn]

This is very good information. Thanks to you all I have decided not to start the motor and blow a 3rd filter and have to pull the motor out to clean again. It is amazing the artistic talents that the person that built this car obviously has but at the same time they used bits and pieces to build what looks like a cool oiling system but failed to adhere to the basic design that Porsche has developed through all the years of racing experience.

[HawgRyder]

If I can help...the pressure side of the pump pushes oil into the bearings, chain tentioners, piston squirters, etc.
The return or scavenge side just returns the oil to the tank...either through the filter...or the coolers (engine mounted or front fender mount)...so...whereas the pressure side builds up pressure by being restricted (oil forced into smaller holes)...the return should not see as high a pressure because it should have almost no restrictions.
It appears that either the filter itself...or something just downstream from it are causing a rise in pressure.
I would trace the lines very carefully to see what has occured.
Perhaps a couple of lines have been accidently exchanged going towards the tank?
Just a thought.
Bob

[KTL]

Shoot us some pictures and we can help you even more. We're responding to your request with our experiences, but seeing what you got in place would make it easier for us to analyze it.

[dsfnctn]

Originally Posted by KTL

Shoot us some pictures and we can help you even more. We're responding to your request with our experiences, but seeing what you got in place would make it easier for us to analyze it.

The car came with an oil filter housing that was a custom unit from a Nissan GTR. It failed and the builder of the car sent the pictured 72 oil filter console as a replacement for the GTR unit. We got it from him as pictured which was supposed to be set up for flow through the filter. I just figured out from all your help that when the oil heated up the thermostat opened up to the port that has the plug in it and shut off the flow thru the filter. that is when the filter blew.
How stupid now that I think about it. Now I will plumb the oil back to the tank when cold and plumb to cooler when hot.

[dsfnctn]

Thanks again for all of your help

[Daves911L]

Man, I'll bet that made one hell of a mess on that purty motor!

[KTL]

If you'd like to eliminate those adapter fittings, BAT makes some nice metric hose ends that don't break the bank. Just make sure to tell them you want the black fittings, not the spendy black & gold ones.

http://97.74.32.155/files/metric.pdf

Also, depending on how your system is plumbed, you may not need the thermostatic function of the '72 oil filter console. Maybe you could use a 964 style t-stat?





I've got one if you'd like to take a look at it. It's of course the piece on the left, not the actual 964 t-stat highlighted on the right!

[AlfonsoR]

Originally Posted by dsfnctn

Where did you get the black diamond stitched engine insulation panel (above the engine)? Hadn't seen that before and it looks really nice.

[KTL]

Yah that's a mean motor just from what we can see in the partial picture.

Slide valve throttles
Twin plug distributor
MFI
226mm "high horsepower" fan

Stitched firewall covering is very sharp indeedy!